Acquired cellular responsiveness in cattle cleared of [formula omitted] 28 months earlier

Abstract

The leukocyte migration inhibition test (LMIT) was used to assess cell-mediated immune responses of cattle against Anaplasma marginale . Leukocytes from 7 of 11 cows that had been cleared of the carrier state by antibiotic therapy 28 months earlier were inhibited from their normal migration by A. marginale antigens ( P <0.001 ). After reexposure to virulent organisms, all animals were positive to the LMIT. There was not a significant relationship (r=0.49) between LMIT values before and after reexposure. Results suggest that animals free of anaplasmosis for more than 2 years are capable of cell-mediated immune responses, despite decreased in vitro responsiveness at the time of reexposure. Acquired cellular responses did not prevent reinfection as all animals became A. marginale carriers.